Hard acid-hard base interactions responsible for densification of alumina layer for superior electrochemical performance

The interactions between hard acid and hard bases during plasma electrolysis (PE) of Al-Mg-Si alloy and their roles in suppressing the localized plasma discharges were investigated. The oxalate and citrate ions during PE acted as strong Lewis bases tended to interact with the strong Lewis acid of interfacial Al+3 ions to formulate a thick adsorbed electrochemical double layer acting as a barrier layer of complex ligand structure. The shielding effect of this layer and its rapid reformation facilitated the formation of defect-free coating showing a superior corrosion performance to other samples.